Ferson



{No Model.)

0. W. JEFFERSON. FLEXIBLE MIGA INSULATING SHEET.

No. 563,379. Patented July 7, 1896.

ca "5W ATTORNEY.

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UNITED STATES PATENT OFFICE.

CHARLES \VILKIN JEFFERSON, OF SOHENEOTADY, NEIV YORK, ASSIGNOR TO THEMIOA INSULATOR COMPANY, OF NEIV YORK, N. Y.

FLEXIBLE MICA INSULATING-SHEET.

SPECIFICATION forming part of Letters Patent No. 563,379, dated July '7,1896. Application filed March 16, 1895. Serial No. 541,998. (No model.)

To aZZ whom it may concern:

Be it known that I, CHARLES IVILKIN J EF- FERSON, a subject of the Queenof Great Britain, and a resident of Schenectady, county of Schenectady,and State of New York, have invented certain new and useful Improvementsin Flexible Mica Insulating-Sheets, (Case No. 0,) of which the followingis a specification.

Heretofore mica sheets were employed for the purpose of electricallyinsulating electrical conductors, as, for example, the laminae offield-magnets, the grooves in armaturecores, commutators, armatures, andother elements employed in manufacturing electrical machinery andinstruments. Difliculties were met in view of the expense of largesheets of mica. Later small mica scales were employed in such a manneras to obtain large workable sheets, for example, as shown in my formerpatents, N 0. 483,653, dated October4, 1892; N 0. 491,707, datedFebruary 14, 1893; No. 491,708, dated February 14, 1893; No. 497,324,dated May 16, 1893, and No. 500,902, dated July 4, 1893.

The invention set forth in the specifications of the above patents havebeen carried out in practice, but certain important difficulties havebeen experienced. In all of the said inventions I employed liquidcement, which, in its cold and dry state, is brittle. I am now able toproduce a product in which the cementing material is dry, in sheet form,pliable and flexible to the highest degree at all ordinary temperatures.

The article forming the basis of my claims is illustrated in theaccompanying drawings, wherein- Figure l is a cross-section of a portionof an insulating-sheet largely magnified in thickness. Fig. 2 is a planof the same. Fig. 3 is a perspective of a mica trough forarmaturegrooves to illustrate one of the forms into which the sheet maybe cut and bent. Fig. 4 is a perspective view of an application of theinvention.

The lowest layer A of the whole sheet is formed of mica scales, of whichthe edges may simply abut, as at A, or overlap each other, as at A.Above this layer of mica is a sheet of fibrous material B, which maybepaper or cloth. Between the fibrous sheet and the mica is whatis knownin commerce as guttapercha tissue 0. Next comes a second tissue D, andthen another mica layer E, and

the layers may be repeated in the same or dif- 5 5 ferent relativeorders until the desired thickness is obtained.

It has been found that if the gutta-percha tissue forms the outercoating of the sheet the finished sheets cannot then be so satisfactory,because when packed away they stick to each other, and also stick toomuch to the articles in which they act as insulators.

The whole product is heated until the gutta percha tissue becomesadhesive, and it is then pressed, and, consequently, when the sheetbecomes cool the layers adhere to one another and form such a flexiblesheet that it can be bent like cloth or paper into any form.

The old product forming the basis of the above-named patents is, ascompared to this new product, hard and stiff, and cannot be bent to anyappreciable extent without break ing unless heat is first applied,whereas the new product can be bent in its cold state as well as the oldproduct can when heated. This is illustrated in Fig. 3, where Hrepresents a trough made by bending the sheet into the U form indicated.

My invention may be modified. For example, the fibrous material may beentirely omitted, so that the sheet consists of, first, a layer of mica,then of the gutta-percha tissue, and then again of mica. It is importantto notice that cloth may be employed among the different layers, but itshould be understood that there is always a layer of gutta-percha tissuebetween any two layers of other material.

In the manufacture and use of underground cables it has been founddifficult to properly protect the electric conductor or cable frommoisture and other conductors which assist in leakage. My invention asabove described solves this problem, as illustrated in the con structionin Fig. 4, where F is a cable, and G is a strip, consisting of alternatelayers of gutta-percha tissue and other materials, as described withreference to any of the preceding figures. This strip is wound aroundthe conductor spirally, so as to form a complete covering.

I claim as my invention 1 An electric insulator, in sheet form,consisting of layers of fibrous and mica sheets, and gutta-percha tissuebetween any and every two of said layers.

2. An electric insulator, in sheet form, consisting of layers of micascales, and adhesive gutta-percha tissue between any and every two ofsaid layers.

3. An electric insulator, in sheet form, consisting of a fibrous sheet,a gutta-percha tissue held thereon by adhesion, mica scales held to thegutta-percha tissue by adhesion, a second sheet of gutta-percha tissueupon the mica, a second sheet of fibrous material upon Witnesses:

WILLIAM R. XVARREN, EMMA O. DEGHNEE.

